1. Field of the Invention
This invention relates generally to pool alarms, and more particularly to an improved swimming pool alarm that is sensitive to wave motion but can discriminate between disturbances caused by entry of a small child or animal into the pool and those caused by wind, rain, and other effects.
2. Description of the Prior Art
Pool alarm systems typically include a transducer placed below the water surface which detects disturbances in the water. Commonly, the transducer is either an acoustic transducer which detects high frequency sound waves in the water, or a pressure transducer which detects low frequency waves. Mechanical vanes and tilt switches have also been employed as transducers in pool alarms. One problem with prior art pool alarm systems is that wave analysis circuitry of the systems is often unable to differentiate between wave motion caused by normal extraneous stimuli (e.g., wind, rain, automatic pool cleaning apparatus) and wave motion caused by entry of a small child or animal into the pool. Several prior art pool alarm systems include wave analysis circuitry for filtering, comparing, and otherwise processing signals generated by the transducer to determine whether a wave disturbance sensed by the transducer is consistent with a wave caused by a child or animal entering the water, in which case an alarm is sounded.
Applicants previous patent, U.S. Pat. No. 5,121,104 discloses a pool alarm including: a pressure transducer responsive to pressure variations and operative to generate a signal representing waves; an amplifier connected to the transducer to set the signal level; a low frequency band pass filter connected to the amplifier output for filtering out wind, rain and pool side traffic; a comparator amplifier for comparing the filter output to a fixed threshold voltage; and a periodicity discriminator to determine if an apparent wave is periodic and if the period is consistent with that of a wave caused by a small child or animal entering the water. If the signal output from the filter exceeds the fixed threshold voltage of the comparator twice within a preset duration of time, an audio alarm is sounded.
One important problem with prior art pool alarm systems is false alarms in response to wind gusts. Also, while strong wind gusts are incident upon a swimming pool, wave motion characterized by wide crests, or swells may be generated such that the entry into the pool of a small child or animal will be obscured and therefore unlikely to be detected. What is needed is a pool alarm system which activates a disturbance warning, distinguishable from the audio alarm indicating entry of a small child or animal into the pool, wherein the disturbance warning is activated in response to a disturbance characterized by wide crests or swells which could obscure the entrance of a small child or animal into the pool.
Another problem with prior swimming pool alarm systems is that the alarm systems may be easily disarmed by a child thereby allowing children or small animals to enter the pool without triggering the alarm. Furthermore, an adult who disarms the alarm system in order to go swimming may forget to turn the alarm back on after swimming.
What is needed is a pool alarm system having a child-proof deactivation procedure. What is also needed is a pool alarm system which automatically turns on after a fixed period of time during which no one is swimming in the pool.
An additional problem with prior art pool alarm systems is that the power supply, usually batteries, may be OFF or may become too low to operate the alarm system. What is needed is a battery operated pool alarm system which periodically indicates to a user that the battery power supply is low so that batteries may be replaced.